The present invention relates to a heat-transfer type thermal recording device which heats an ink film tape with a thermal head to soften the ink enabling transfer of the ink onto recording paper. Specifically, the present invention relates to a cassette device containing an ink film tape for use in a line-format thermal recording device and the specific paper-feeding method employed in such a line-format thermal recording device.
Recently, a wide variety of compact-size and low-cost color hard copying machines including heat-transfer type thermal recording devices have been developed. These heat-transfer type thermal recording devices first heat the ink film tape, softening the ink to enable transfer onto standard recording paper. Ink is printed on each picture by overlapping a variety of colors in the order of yellow (Y), magenta (M), cyan (C), and black (B) in a method conventionally called the "sequential picture coloration system".
In conventional machines, the ink film tape which contains yellow (Y), magenta (M), cyan (C), and black (B) colors in sequence moves forward while the paper must move backward and forward to allow the sequential printing of each color overlapping them to achieve the desired final shade.
One of the prior art devices featuring the above mechanism is the configuration shown in FIG. 3 and described below. Reference number 31 indicates the drive roller, which is connected to the drive source via drive pulley 32 and provided with teeth 31A, each being engaged with perforations 33A and 33B on either side of the recording paper. The recording paper 33 is conveyed from a paper-feeding sprocket 34, which rotates in synchronism by pulley with the drive roller 31, and passes under the drive roller 31 and then over its upper side. The supply reel 35 is loaded with the ink film tape 36. After being drawn from the supply reel 35, the ink film tape 36 passes between the recording paper 33 and the drive roller 31 before being wound onto the take-up reel 37 which is connected to the drive motor 38. A line-format thermal head 39 is installed in a position below the drive roller 31. The thermal head 39 is pressed against the recording paper 33 on the drive roller 31 during the recoding operation. This causes the ink to soften and be transferred onto the recording paper 33. These conventional thermal recording devices require complex operations prior to printing, namely the ink film tape wound on the supply reel needs to be drawn from this reel and passed through the drive roller and thermal head before it is retrieved on the take-up reel. The operations of loading and unloading the ink film tape are unnecessarily complicated; furthermore, the tape is easily creased or damaged during these operations.
When operating the conventional thermal recording device shown in FIG. 3, the following process must be followed. The recording paper 33 moves forward and backward according to the rotation of drive roller 31 and by means of edge perforations 33A and 33B and teeth 31A and 31B. Power is provided to drive roller 31 through drive pulley 32. The recording paper 33 is conveyed from the paper-feeding sprocket 31 which rotates in synchronism by pulley with the drive roller 31, passes under the driver roller 31 and to its upper side. The ink film tape 36, simultaneously drawn from the supply roller 35, passes through the drive roller 31 along a path below the recording paper 33 and is then wound onto the take-up reel 37 which is connected to the drive motor 38. In addition, the line-format thermal head 39 is installed in a position below and close to the drive roller 31. The thermal head 39 is pressed against the recording paper 33 on the drive roller 31 while the recording operation is underway, thus causing the ink to soften and to be adequately transferred onto the recording paper 33. To successfully print using this conventional thermal recording device, the recording paper 33 must move back and forth three or four times, so that the colors are applied in sequence, overlapping yellow (Y), magenta (M), cyan (C), and black (B) until the desired shade is achieved. If the recording paper 33 is not fed through rollers precisely, unwanted shades and imprecise delineation of color on the recording paper 33 will result. When operating a thermal recording device capable of printing with a discrimination of 10 dots per millimeter as a line-format device to print successive colors, only +0.05 mm of color deviation per dot is permissible without poor quality printing. Even though conventional tractor-feed format type machines are effective against paper skewing, they are not able to feed the recording paper with the precision necessary for printing successive colors due to employing a recording paper clamping mechanism. Conventional machines, other than tractor-format types, employ platen rollers, but these machines have problems such as skewing or slippage of recording paper, and are thus unable to feed paper with the precision necessary to print successive colors.